1. Field of the Invention
This invention relates generally to robotic arms, and more particularly to robotic arms for lifting, moving, and placing semiconductor wafers.
2. Description of the Prior Art
Solid state electronic devices are made from semiconducting materials such as silicon, germanium, and gallium arsenide. The semiconducting materials are "grown" by placing a seed of semiconducting material having the correct crystal structure into a vat of melted semiconductor material and then slowly withdrawing the seed from the vat to form a long, tubular slug of material. The slug is then sliced into thin wafers which are further processed to make the final semiconductor devices.
The semiconductor manufacturing industry is becoming more and more competitive. It therefore behooves semiconductor manufacturers to increase productivity by reducing labor costs, and to minimize damage and contamination during the processing of the semiconductor devices.
One way to accomplish both of these goals is to automate the wafer handling process. For example, if a robot arm can be used to transfer wafers in and out of a cassette, or to perform similar tasks, labor costs and the possibility of human contamination of the wafers are greatly reduced.
There are many examples of robotic-type assemblies designed to handle semiconductor wafers. For example, in U.S. Pat. No. 4,108,323 of Shambelan et al. an apparatus is disclosed which has a wafer handling arm which moves a paddle in and out of a cassette to pick up or deposit a semiconductor wafer. Another example can be found in U.S. Pat. No. 4,427,332 of Manrikuez which teaches a wafer transfer device having a paddle which lifts a wafer from a cassette and positions it under an inspection microscope. Furthermore, U.S. Pat. No. 4,501,527 of Jacoby et al., U.S. Pat. No. 3,823,836 Cheney et al., and Western Electric Technical Digest #49 (January, 1978) all teach pivoting arms having vacuum paddles which can remove a wafer from a cassette and transfer it to a work station. Finally, U.S. Pat. No. 4,457,661 of Flint et al. teaches a wafer loading apparatus which includes processing trays mounted on a generally cylindrical carousel. Wafers are transferred in and out of the cassettes with vacuum paddles.
A problem with wafer transfer arms of the prior art is that they tend to be specialized pieces of equipment, and are not well adapted for use as original equipment manufacturer (OEM) subassemblies. As such, they are often manufactured on an individual basis, and thus tend to be expensive.
Another problem with wafer transfer arms of the prior art is that they are not particularly compact in construction. The mechanisms of the wafer transfer arms of the prior art often require housings which are much longer than the length of their stroke.
Another problem with wafers transfer arms of the prior art is that they often contaminate the semiconductor wafers that they are transporting. This is due primarily to the fact that the mechanisms which operate the wafer transfer arms are often quite close to the wafers being transported, allowing grease, fumes, etc. to contaminate the wafers.